1. Field of the Invention
The present invention relates to a process for preparing a catalyst system for olefin polymerization which is obtainable by bringing at least one metallocene, at least one organometallic compound, at least one compound that is obtainable by a reaction of an organometallic compound with an organic compound bearing a functional group containing active hydrogen, at least one Lewis base and at least one support into contact with one another, to catalyst systems obtainable by this process, to the use of these catalyst systems for olefin polymerizations, to a process using such catalyst systems for polymerization and copolymerisation of olefins and to polymers which are prepared using such catalyst systems.
2. Background of the Art
Processes for preparing polyolefins using soluble, homogeneous catalyst systems comprising organic transition metal compounds such as metallocene complexes are well known (Angew. Chem. 1995, 107, 1255-1283 or U.S. Pat. Nos. 4,752,597; 5,017,714; 5,391,790; 5,616,747 or EP Patent Nos. 0 320 762; 0 416 815; 0 537 686 and 0 669 340). They may be produced, for example, by reacting cyclopentadienyl metal compounds with halides of transition metals, such as titanium, zirconium, and hafnium.
It is also well known that basic properties of the metallocenes, such as polymerization activity, stereoselectivity, regioselectivity, and maximum achievable polymer molecular weight can be systematically controlled by specific substitution patterns of the ligand sphere. However, to use metallocenes for the stereoselective and regioselective polymerization of olefins, the preparation of the isomerically pure racemic form is absolutely necessary, since the corresponding meso form produces undesired atactic polymer, like atactic polypropylene. The isomerically pure racemic form is understood to mean a rac:meso ratio of at least 5, and preferably 10.
Such stereoselective and/or regioselective metallocenes for the polymerization of olefins to polyolefins especially for the polymerization of propylene or the copolymerization of propylene with other olefins and which are useful and preferred as metallocenes for the catalyst systems of the present invention, are well known in the literature. As an example, such metallocenes are disclosed in U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910; 4,808,561; 4,871,705; 4,931,417; 4,933,403; 4,937,299; 5,017,714; 5,026,798; 5,057,475; 5,120,867; 5,132,381; 5,145,819; 5,155,180; 5,198,401; 5,239,022; 5,243,001; 5,276,208; 5,278,119; 5,296,434; 5,304,614; 5,324,800; 5,328,969; 5,329,033; 5,350,723; 5,374,752; 5,391,790; 5,416,178; 5,436,305; 5,455,366; 5,510,502; 5,532,396; 5,543,373; 5,554,704; 5,576,260; 5,612,428; 5,616,663; 5,629,254; 5,635,437; 5,661,096; 5,672,668; 5,679,812; 5,723,640; 5,739,366; 5,741,868; 5,770,753; 5,786,432; 5,830,821; 5,840,644; 5,840,948; 5,852,142; 5,929,264; 5,932,669; 6,017,841; 6,051,522; 6,051,727; 6,057,408; 6,087,291; 6,100,214; 6,114,479; 6,117,955; 6,124,230; 6,140,432; 6,194,341; 6,218,558; 6,228,795; 6,242,544; 6,245,706; 6,252,097; 6,255,506; 6,255,515; 6,376,407; 6,376,408; 6,376,409; 6,376,410; 6,376,411; 6,376,412; 6,376,413; 6,376,627; 6,380,120; 6,380,121; 6,380,122; 6,380,123; 6,380,124; 6,380,330; 6,380,331; 6,380,334; 6,399,723; 6,444,606; 6,469,114 and U.S. Application Nos. 2001021755; 20030149199 and EP 576 970; EP 611 773, and WO 97/32906; WO 98/014585; WO 98/22486; WO 00/12565; WO 01/48034; WO 03/045964; WO 03/106470.
The interest in these homogeneous single site catalysts originates from the ability to produce polyolefins that can not be synthesized by using conventional Ziegler-Natta catalyst, for example polyolefins having a very narrow molar mass distribution and a uniform comonomer content. In order to obtain active catalysts for olefin polymerizations the metallocene complexes have to be reacted with a cocatalyst. The most frequently used cocatalysts consist of aluminoxanes, such as methylaluminoxane. The disadvantage of these cocatalysts is that they have to be used in large excess. Therefore these catalyst systems are quite expensive. Other type of cocatalysts exist that convert the metallocene complexes into cationic complexes. These type of cocatalysts can be used in stoichiometric or virtually stoichiometric ratios (Chem. Rev. 2000, 100, 1391-1434).
In polymerizations using such soluble, homogeneous catalyst systems, heavy deposits are formed on reactor walls and the stirrer if the polymer is obtained as a solid. These deposits are formed by agglomeration of the polymer particles whenever metallocene and/or cocatalyst are present in dissolved form in the suspension. The deposits in the reactor systems quickly reach considerable thickness and have a high strength. They prevent heat exchange to the cooling medium and therefore have to be removed regularly. Such homogeneous catalyst systems cannot be used industrially in liquid monomer or in the gas phase. To avoid deposit formation in the reactor, supported catalyst systems in which the metallocene and/or the cocatalyst is/are fixed on an inorganic support material have been proposed. As an example, in EP-A-0 576 970 or WO 01/48034 metallocenes and corresponding supported catalyst systems are disclosed. Such supported catalyst systems give polymers, in particular polypropylenes, having melting points of up to about 156° C.
Furthermore industrial utilization of metallocene catalysts requires the catalyst system to be made heterogeneous in order to achieve an appropriate morphology of the resulting polymer. It has been shown advantageous to covalently fix the components of the catalyst system to the support. This avoids the detachment of the of the catalyst system from the support which leads to homogeneous polymerisations and unsatisfactory polymer morphology.
WO 96/04319, WO 96/23005 and WO 99/33881 describe catalyst systems in which the cocatalyst, a Lewis acid like tris(pentafluorophenyl)borane, is covalently bound to the support material. However these catalyst systems have a low polymerisation activity and no organic compounds having functional groups containing active hydrogen are used for the preparation of the catalyst system.
The patents WO 99/40129, WO 00/62928 and WO 01/47635 teach the use of a Lewis-base, a compound that is obtainable by a reaction of an organometallic compound with an organic compound bearing a functional group containing active hydrogen, a metallocene, and a support as components of the catalyst system. The patents WO 04/007570 and WO 04/007569 teach the preparation of similar catalysts systems by a simpler process that requires fewer purification steps. However all of these catalyst systems still show a rather low polymerisation activity.
It is an object of this invention to provide a catalyst system which avoids the disadvantages of the prior art and furthermore has an increased polymerisation activity, guarantees good polymer morphology and leads to polymerisations without formation of deposits in the reactor.
We have found that this object is achieved by a catalyst system based on a specific stoichiometric ratio of the catalyst components, which unexpectedly displays very high polymerization activities and gives a good polymer morphology.